Abaixo está uma instrução que descreve uma tarefa de geração de SQL, combinada com uma entrada que fornece mais contexto sobre os esquemas de tabela disponíveis. Escreva o código SQL que responda adequadamente à solicitação
 ###Instrução: Qual é o número total de Ano(s), quando a Data (Abertura) é "21 de setembro"?
 ###Tabelas: CREATE TABLE history (history_id AUTO_INCREMENT PRIMARY KEY, Year INT, Date (Opening) VARCHAR, Date (Closing) VARCHAR, Opening Film VARCHAR, Number of Screening VARCHAR) CREATE TABLE 2010_lightweight_manx_grand_prix_practice_times__&__leaderboard (2010_lightweight_manx_grand_prix_practice_times__&__leaderboard_id AUTO_INCREMENT PRIMARY KEY, Rank INT, Rider VARCHAR, Sat 21 Aug VARCHAR, Mon 23 Aug VARCHAR, Tues 24 Aug VARCHAR, Wed 25 Aug VARCHAR, Thurs 26 Aug VARCHAR, Fri 27 Aug VARCHAR, Sat 29 Aug VARCHAR) CREATE TABLE head_coaching_history (head_coaching_history_id AUTO_INCREMENT PRIMARY KEY, Name VARCHAR, Years VARCHAR, Wins INT, Losses INT, Ties INT, Pct. INT) CREATE TABLE managerial_changes (managerial_changes_id AUTO_INCREMENT PRIMARY KEY, Team VARCHAR, Outgoing manager VARCHAR, Manner of departure VARCHAR, Date of vacancy VARCHAR, Replaced by VARCHAR, Date of appointment VARCHAR) CREATE TABLE composition_of_the_6th_seanad (composition_of_the_6th_seanad_id AUTO_INCREMENT PRIMARY KEY, Administrative Panel INT, Agricultural Panel INT, Cultural and Educational Panel INT, Industrial and Commercial Panel INT, Labour Panel INT, National University of Ireland INT, University of Dublin INT, Nominated by the Taoiseach INT, Total INT)  
SELECT COUNT Year FROM history WHERE Date (Opening) = september 21